Thin film transistor, flat panel display including the thin film transistor, and method for manufacturing the thin film transistor and the flat panel display

ABSTRACT

A thin film transistor having a transformed region that provides the same result as patterning a semiconductor layer, a flat panel display having the thin film transistor and a method for manufacturing the thin film transistor and the flat panel display are disclosed. The thin film structure includes a gate electrode, a source and a drain electrode, each insulated from the gate electrode and an organic semiconductor layer coupled to the source electrode and the drain electrode. The organic semiconductor layer includes the transformed region having a crystal structure distinguished from crystal structures of regions around the channel region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit under 35U.S.C. §120 of U.S. application Ser. No. 11/298,211, filed Dec. 9, 2005,which is hereby incorporated in its entirety by reference. Thisapplication and U.S. application Ser. No. 11/298,211 claim the benefitof Korean Patent Application No. 10-2004-0111097, filed on Dec. 23,2004, in the Korean Intellectual Property Office, the disclosure ofwhich is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present embodiments relate to a thin film transistor (TFT), a flatpanel display having the TFT and a method for manufacturing the TFT andthe flat panel display; and more particularly, to a thin film transistor(TFT) having a transformed region in an organic semiconductor layer thatprovides the same result as patterning the organic semiconductor layer,a flat panel display having the TFT and a method for manufacturing theTFT and the flat panel display.

2. Description of the Related Art

A thin film transistor (TFT) has been used in a flat panel display as aswitching element for controlling operations of each pixel or as adriving element for operating a pixel. The TFT includes a liquid crystaldisplay element, an organic electroluminescent display element and aninorganic light emitting display element.

The TFT includes an active layer having a source region and a drainregion which are doped with a high concentration of impurity and achannel region formed between the source region and the drain region.The TFT also includes a gate electrode formed on a predetermined regionof a substrate where the channel region is faced and the gate electrodeis insulated from the active layer. The TFT further includes a sourceelectrode coupled to the source region and a drain electrode, eachcoupled to the drain region.

The flat panel display has become thinner and has been required to haveflexibility.

For manufacturing thinner flat panel displays having flexibility, aplastic substrate has been used as a substrate of the flat panel displayinstead of a glass substrate. When using a plastic substrate, a hightemperature thermal process cannot be performed in manufacturing theflat panel display. Accordingly, there are difficulties in using aconventional polysilicon thin film transistor for manufacturing the flatpanel display.

To overcome the above problem, an organic semiconductor has been used.The organic semiconductor can be formed in a low temperature thermalprocess for manufacturing a thin film transistor (TFT) which isrelatively inexpensive.

However, a photo lithographing method cannot be used for patterning theorganic semiconductor layer. In other words, the pattern is formed onthe organic semiconductor forming an active channel. If a combinationmethod of a wet type and a dry type of etching methods is used forforming the pattern on the organic semiconductor, the organicsemiconductor is damaged.

Therefore, a new method for patterning the organic semiconductor isneeded.

SUMMARY OF THE INVENTION

One embodiment relates to a thin film transistor, comprising:

-   -   a gate electrode;    -   a source electrode and a drain electrode, each insulated from        the gate electrode; and    -   an organic semiconductor layer insulated from the gate electrode        and coupled to the source electrode and the drain electrode,    -   wherein the organic semiconductor layer comprises a transformed        region around at least a channel region, the transformed region        having a crystal structure distinguished from other regions.

In one aspect, the crystal size of the transformed region is smallerthan the crystal size of the other regions.

In another aspect, the transformed region has lower current mobilitythan the other regions.

In yet another aspect, the transformed region is formed by emittinglight on a predetermined region where the transformed region is formed.

In still another aspect, the transformed region is formed by performinga thermal process on a predetermined region where the transformed regionis formed.

In another aspect, the transformed region comprises a boundary having aclosed curve shape surrounding at least the channel region.

In another aspect, the transformed region comprises a boundary formed onat least one pair of substantially parallel lines where at least thechannel region is located between the substantially parallel lines.

In another aspect, the transformed region comprises a boundarysubstantially parallel to a line connecting the source region, thechannel region and the drain region.

In another aspect, an insulation layer is formed covering the gateelectrode, and the organic semiconductor layer is formed on theinsulation layer.

Another embodiment relates to an insulation layer covering the gateelectrode; wherein, the source electrode and drain electrode are eachformed on the insulation layer;

-   -   a passivation layer covering the insulation layer, the source        electrode and the drain electrode; wherein, the passivation        layer has an opening over the source electrode or the drain        electrode, wherein the organic semiconductor layer is formed on        the passivation layer.

In another aspect, the source electrode and drain electrode are eachformed on a substrate and the organic semiconductor layer is formed onthe substrate so as to cover the source electrode and drain electrode.

In yet another aspect, the organic semiconductor layer is formed on asubstrate, and the source electrode and the drain electrode are eachformed on the organic semiconductor layer.

In still another aspect, the organic semiconductor layer comprises atleast one of pentacene, tetracene, anthracene, naphthalene,alpha-6-thiophene, alpha-4-thiophene, perylene and its derivatives,rubrene and its derivatives, coronene and its derivatives, perylenetetracarboxylic diimide and its derivatives, perylene tetracarboxylicdianhydride and its derivates, oligonaphthalene and its derivatives,oligothiophene of alpha-5-thiophene and its derivatives, phthalocyanineincluding metal and its derivates, phthalocyanine not including metaland its derivates, naphthalene tetracarboxylic diimide and itsderivatives, naphthalene tetracarboxylic dianhydride and itsderivatives, pyromellitic dianhydride and its derivatives, pyromelliticdiimide and its derivatives, conjugated polymer containing thiophene andits derivatives and polymer containing fluorene and its derivatives.

Another embodiment relates to a flat panel display, comprising:

-   -   a substrate;    -   at least one thin film transistor, each of which is formed on        the substrate and comprises a gate electrode, a source electrode        and a drain electrode, each insulated from the gate electrode        and an organic semiconductor layer coupled to the source        electrode and the drain electrode and insulated from the gate        electrode; and    -   a pixel electrode electrically connected to at least one of the        source and the drain electrodes of the thin film transistor,    -   wherein the organic semiconductor layer comprises a transformed        region around at least the channel region of the organic        semiconductor layer, wherein the transformed region has a        crystal structure which differs from other regions of the        organic semiconductor layer.

In one aspect, the crystal size of the transformed region is smallerthan a crystal size of the other regions.

In another aspect, the transformed region has lower current mobilitythan the other regions.

In yet another aspect, the transformed region is formed by irradiating apredetermined region with light where the transformed region is formed.

In still another aspect, the transformed region is formed by performinga thermal process on a predetermined region where the transformed regionis to be formed.

In another aspect, the transformed region comprises a boundary having aclosed curve shape surrounding at least the channel region.

In another aspect, the transformed region comprises a boundary formed onat least one pair of substantially parallel lines wherein at least thechannel region is located between the substantially parallel lines.

In another aspect, the transformed region comprises a boundarysubstantially parallel to a line connecting to the source region, thechannel region and the drain region.

In another aspect, an insulation layer is formed for covering the gateelectrode and the organic semiconductor layer is formed on theinsulation layer.

Another embodiment relates to an insulation layer covering the gateelectrode; wherein, the source electrode and drain electrode are eachformed on the insulation layer;

-   -   a passivation layer covering the insulation layer, the source        electrode and the drain electrode, wherein the passivation layer        has an opening over the source electrode or the drain electrode;        wherein,    -   the organic semiconductor layer is formed on the passivation        layer.

In another aspect, the source electrode and drain electrode are eachformed on a substrate and the organic semiconductor layer is formed onthe substrate so as to cover the source electrode and drain electrode.

In yet another aspect, the organic semiconductor layer is formed on asubstrate, and the source electrode and the drain electrode are eachformed on the organic semiconductor layer.

In still another aspect, the organic semiconductor layer comprises atleast one of pentacene, tetracene, anthracene, naphthalene,alpha-6-thiophene, alpha-4-thiophene, perylene and its derivatives,rubrene and its derivatives, coronene and its derivatives, perylenetetracarboxylic diimide and its derivatives, perylene tetracarboxylicdianhydride and its derivates, oligonaphthalene and its derivatives,oligothiophene of alpha-5-thiophene and its derivatives, phthalocyanineincluding metal and its derivates, phthalocyanine not including a metaland its derivates, naphthalene tetracarboxylic diimide and itsderivatives, naphthalene tetracarboxylic dianhydride and itsderivatives, pyromellitic dianhydride and its derivatives, pyromelliticdiimide and its derivatives, conjugated polymer containing thiophene andits derivatives and polymer containing fluorene and its derivatives.

Another embodiment relates to a method of manufacturing a thin filmtransistor comprising a gate electrode, a source electrode and a drainelectrode, each insulated from the gate electrode; and an organicsemiconductor layer insulated from the gate electrode and coupled to thesource and the drain electrodes,

-   -   the method comprises irradiating with light the area around at        least a channel region of the organic semiconductor layer        wherein the conductivity of the organic semiconductor layer is        reduced.

In one aspect, the organic semiconductor layer is irradiated by a laser.

In another aspect, the organic semiconductor layer is irradiated withultraviolet light.

In yet another aspect, the organic semiconductor layer comprises atleast one of pentacene, tetracene, anthracene, naphthalene,alpha-6-thiophene, alpha-4-thiophene, perylene and its derivatives,rubrene and its derivatives, coronene and its derivatives, perylenetetracarboxylic diimide and its derivatives, perylene tetracarboxylicdianhydride and its derivates, oligonaphthalene and its derivatives,oligothiophene of alpha-5-thiophene and its derivatives, phthalocyanineincluding a metal and its derivates, phthalocyanine not including ametal and its derivates, naphthalene tetracarboxylic diimide and itsderivatives, naphthalene tetracarboxylic dianhydride and itsderivatives, pyromellitic dianhydride and its derivatives, pyromelliticdiimide and its derivatives, conjugate polymer containing thiophene andits derivatives and polymer containing fluorene and its derivatives.

Another embodiment relates to a method of manufacturing a thin filmtransistor comprising a gate electrode; a source electrode and a drainelectrode, each insulated from the gate electrode; and an organicsemiconductor layer insulated from the gate electrode and coupled to thesource and drain electrodes,

-   -   the method comprises performing a thermal process on the organic        semiconductor layer at least near a channel region of the        organic semiconductor layer after forming the organic        semiconductor layer, wherein the conductivity of the organic        semiconductor layer is reduced.

In one aspect, the organic semiconductor layer comprises at least one ofpentacene, tetracene, anthracene, naphthalene, alpha-6-thiophene,alpha-4-thiophene, perylene and its derivatives, rubrene and itsderivatives, coronene and its derivatives, perylene tetracarboxylicdiimide and its derivatives, perylene tetracarboxylic dianhydride andits derivates, oligonaphthalene and its derivatives, oligothiophene ofalpha-5-thiophene and its derivatives, phthalocyanine including a metaland its derivates, phthalocyanine not including a metal or not and itsderivates, naphthalene tetracarboxylic diimide and its derivatives,naphthalene tetracarboxylic dianhydride and its derivatives,pyromellitic dianhydride and its derivatives, pyromellitic diimide andits derivatives, conjugate polymer containing thiophene and itsderivatives and polymer containing fluorene and its derivatives.

Another embodiment relates to a method of manufacturing a flat paneldisplay, comprising:

-   -   forming a thin film transistor comprising a gate electrode        formed on a substrate; a source electrode and a drain electrode,        each insulated from the gate electrode; and an organic        semiconductor layer insulated from the gate electrode and        coupled to the source and drain electrodes; and    -   forming a pixel electrode electrically connected to one of the        source and the drain electrodes of the thin film transistor,    -   the method comprises irradiating with light the area around at        least a channel region of the organic semiconductor layer        wherein the conductivity of the organic semiconductor layer is        reduced.

In one aspect, the organic semiconductor layer is irradiated with alaser.

In another aspect, the organic semiconductor layer is irradiated withultraviolet light.

In yet another aspect, the organic semiconductor layer comprises atleast one of pentacene, tetracene, anthracene, naphthalene,alpha-6-thiophene, alpha-4-thiophene, perylene and its derivatives,rubrene and its derivatives, coronene and its derivatives, perylenetetracarboxylic diimide and its derivatives, perylene tetracarboxylicdianhydride and its derivates, oligonaphthalene and its derivatives,oligothiophene of alpha-5-thiophene and its derivatives, phthalocyanineincluding a metal and its derivates, phthalocyanine not including metaland its derivates, naphthalene tetracarboxylic diimide and itsderivatives, naphthalene tetracarboxylic dianhydride and itsderivatives, pyromellitic dianhydride and its derivatives, pyromelliticdiimide and its derivatives, conjugate polymer containing thiophene andits derivatives and polymer containing fluorene and its derivatives.

Another embodiment relates to a method of manufacturing a flat paneldisplay, comprising:

-   -   forming a thin film transistor comprising a gate electrode        formed on a substrate, a source electrode and a drain electrode,        each insulated from the gate electrode; and an organic        semiconductor layer insulated from the gate electrode and        coupled to the source and the drain electrodes; and    -   forming a pixel electrode electrically connected to one of the        source and the drain electrodes of the thin film transistor,    -   the method comprises performing a thermal process on the organic        semiconductor layer at least near a channel region of the        organic semiconductor layer after forming the organic        semiconductor layer, wherein the conductivity of the organic        semiconductor layer is reduced.

In one aspect, the organic semiconductor layer comprises at least one ofpentacene, tetracene, anthracene, naphthalene, alpha-6-thiophene,alpha-4-thiophene, perylene and its derivatives, rubrene and itsderivatives, coronene and its derivatives, perylene tetracarboxylicdiimide and its derivatives, perylene tetracarboxylic dianhydride andits derivates, oligonaphthalene and its derivatives, oligothiophene ofalpha-5-thiophene and its derivatives, phthalocyanine including metaland its derivates, phthalocyanine not including metal and its derivates.naphthalene tetracarboxylic diimide and its derivatives, naphthalenetetracarboxylic dianhydride and its derivatives, pyromelliticdianhydride and its derivatives, pyromellitic diimide and itsderivatives, conjugate polymer containing thiophene and its derivativesand polymer containing fluorene and its derivatives.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present embodimentswill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a cross sectional view of a thin film transistor in accordancewith one embodiment;

FIG. 2 is a cross sectional view of the thin film transistor of FIG. 1which shows a method for manufacturing the thin film transistor inaccordance with an embodiment;

FIG. 3 is a cross sectional view of the thin film transistor of FIG. 1which shows a method for manufacturing the thin film transistor inaccordance with another embodiment;

FIGS. 4 through 17 are diagrams showing various patterns of transformedregion;

FIGS. 18 through 21 are cross sectional views of thin film transistorshaving various lamination structures in accordance with the presentembodiments; and

FIG. 22 is a cross sectional view of an organic light emitting displayhaving a thin film transistor of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The present embodiments will now be described more fully with referenceto the accompanying drawings, in which exemplary embodiments are shown.

FIG. 1 is a cross sectional view of a thin film transistor (TFT) inaccordance with one embodiment.

As shown in FIG. 1, TFTs 10 and 10′ are formed on a substrate 11. Aflexible substrate may be used as the substrate 11. That is, a plasticsubstrate may be used as the substrate 11. However, the presentembodiments are not limited to the use of a plastic substrate. Anyflexible substrate can be used as the substrate 11 such as apredetermined thickness of flexible substrate made by a glass materialor a metal material.

As shown in FIG. 1, the TFTs 10 and 10′ are formed on the substrate 11and they are adjacent. Also, TFTs 10 and 10′ have substantiallyidentical structure. Hereinafter, the structure of TFT 10 is explained.

A gate electrode 12 having a predetermined pattern is formed on thesubstrate 11 and a gate insulation layer 13 is formed to cover the gateelectrode 12. A source electrode and a drain electrode 14 are eachformed on the gate insulation layer 13. As shown in FIG. 1, the sourceelectrode and the drain electrode 14 may be formed to overlap with apredetermined part of the gate electrode 12. However, the presentembodiments are not limited to having the source electrode and the drainelectrode 14 overlapping with the gate electrode 12. An organicsemiconductor layer 15 is formed on the source electrode and the drainelectrode 14 to cover the entire surface of the TFT 10.

The organic semiconductor layer 15 includes a source and a drain region15 b and a channel region 15 a connecting the source and the drainregions 15 b. An n-type organic semiconductor or a p-type organicsemiconductor may be used for the organic semiconductor layer 15. Also,an n-type impurity or a p-type impurity may be doped on the source andthe drain regions 15 b.

The organic semiconductor layer 15 is formed by using organicsemiconductor material including, for example, pentacene, tetracene,anthracene, naphthalene, alpha-6-thiophene, alpha-4-thiophene, peryleneand its derivatives, rubrene and its derivatives, coronene and itsderivatives, perylene tetracarboxylic diimide and its derivatives,perylene tetracarboxylic dianhydride and its derivates, aoligonaphthalene and its derivatives, oligothiophene ofalpha-5-thiophene and its derivatives, phthalocyanine including a metal(e.g. Cu, Pt, etc) and its derivatives, phthalocyanine not including ametal (e.g. Cu, Pt, etc) and its derivates, naphthalene tetracarboxylicdiimide and its derivatives, naphthalene tetracarboxylic dianhydride andits derivatives, pyromellitic dianhydride and its derivatives,pyromellitic diimide and its derivatives, a conjugate polymer containingthiophene and its derivatives and a polymer containing fluorene and itsderivatives.

As shown in FIG. 1, the organic semiconductor layer 15 is entirelyevaporated on the TFTs 10 and 10′ to cover the entire surface of the TFT10 and TFT 10′. Therefore, if patterning of the organic semiconductorlayer 15 is not performed, it may generate cross-talk between TFTs 10and 10′.

For preventing generation of cross-talk between the TFTs 10 and 10′, atransformed region 15 c is formed between the TFTs 10 and 10′ in thepresent embodiments. The transformed region 15 c is a predeterminedregion of the organic semiconductor layer 15 which is transformed tohave a crystal structure different from other regions of the organicsemiconductor layer 15.

In a view of single TFT 10, the transformed region 15 c is formed aroundat least the channel region 15 a. The transformed region 15 c providesthe same result as patterning the organic semiconductor layer 15.

A predetermined region of the semiconductor layer 15 is decomposed,phase transited or photo-oxidized to form the transformed region 15 c.That is, by decomposing, phase transiting or photo-oxidizing, a crystalstructure of the predetermined region becomes modified. In oneembodiment, the predetermined region of the organic semiconductor layer15 is irradiated with light to modify the crystal structure of thepredetermined region of the organic semiconductor layer 15 as shown inFIGS. 2 and 3.

FIG. 2 is a cross sectional view of a thin film transistor fordemonstrating a method for forming a transformed region 15 c byirradiating a predetermined region of an organic semiconductor layer 15with a laser and FIG. 3 is a cross sectional view of a thin filmtransistor for demonstrating a method forming a transformed region 15 cby exposing a predetermined region of an organic semiconductor layer 15to ultraviolet (UV) rays.

As shown in FIG. 2, if the predetermined region of the organicsemiconductor layer 15 is irradiated with a laser, the crystal structureof the predetermined region is changed by the heat locally generated bythe laser. That is, the heat generated by the laser decomposes,photo-oxidizes or phase-transits the crystal structure of thepredetermined region to be different from other regions of the organicsemiconductor layer 15 (e.g. having a smaller crystal size).

As shown in FIG. 3, a mask 40 having a shielding portion 41 and anopening portion 42 is arranged above the TFTs 10 and 10′ within apredetermined space and the mask 40 is irradiated with light. Theopening portion 42 passes the radiated UV rays to the predeterminedregion of the organic semiconductor layer 15 and the shielding portion41 blocks the UV rays irradiating the organic semiconductor layer 15.The predetermined region of the organic semiconductor layer 15 isexposed to the UV rays and the crystal structure of the predeterminedregion is changed by being decomposed, phase-transited orphoto-oxidized. The crystal structure of the predetermined regionbecomes different from crystal structures of other regions of theorganic semiconductor layer 15.

One characteristic of the transformed region 15 c formed by the abovementioned methods becomes different from the other regions of theorganic semiconductor layer 15. That is, the size of the crystal of thetransformed layer 15 c becomes smaller compared to crystals of otherregions.

The transformed region 15 c is formed on the organic semiconductor layer15 for blocking crosstalk between TFTs 10 and 10′.

Degeneration of an organic material in the organic semiconductor layer15 causes an increase in resistance. That is, when the size of thecrystals of organic material in the organic semiconductor layer 15becomes smaller, the resistance of the degenerated organic materialincreases. Accordingly, the degenerated organic material becomes anobstacle to transferring the carrier. Therefore, the degenerated organicmaterial provides the same result as patterning the organicsemiconductor layer to block carrier transferring between adjacent TFTs.

After a laser is directed to a predetermined region of the organicsemiconductor layer 15, the carrier mobility of the predetermined regionsignificantly decreases. This is disclosed by J. Picker in AppliedPhysics Letters, vol. 85, pp. 1377-1379, 2004 (hereinafter “Fisher”).

In one embodiment, the method of Picker is used for obtaining the sameresult as patterning the organic semiconductor layer 15. That is, thelaser is locally directed to a predetermined region of the organicsemiconductor layer 15 for forming the transformed layer 15 c. Thetransformed layer 15 c blocks carrier transfer between adjacent TFTs.The transformed layer 15 c provides the same result as patterning theorganic semiconductor layer 15.

The transformed layer 15 c can be formed by various other methods inaddition to the method of Ficker supra.

It is known that if heat is applied to a pentacene layer evaporated innormal temperature, the crystallinity of the pentacene layer ismaximized when the temperature becomes about 60° C., and a size ofcrystal grain becomes smaller and roughness of surface of the pentacenelayer increases when the temperature increases over 80° C. (Rongbin Ye,Jpn. J. Appl. Phys. Vol. 42 (2003), pp. 4473-4475.)

Furthermore, it has been disclosed that characteristics of elementsbecome degraded since the morphology is modified by annealingalpha-sexithienyl (a-6T) at 90° C. (F. Dinelli Synthetic Metals 146, pp.373-376, 2004.) Moreover, if poly 3-hexylthiophene is annealed at hightemperature, the poly 3-hexylthiophene is easily oxidized and theelement characteristics become degraded in the article. (Brains A.Matties et. al., Mat. Res. Soc. Symp. Proc. Vol. 771 (2003), L10.35.1.)

Based on the above mentioned facts, the transformed region 15 c may beformed by locally performing a thermal process on a predetermined regionof the organic semiconductor layer. That is, if a region correspondingto the transformed layer 15 c of the organic semiconductor layer 15 islocally thermal processed, the region of the organic semiconductor layer15 is transformed so that the transformed region 15 c is has degradedcharacteristics, that is it has lowered carrier mobility.

The local thermal process may be performed by irradiating light, such asUV rays, to a predetermined region of the organic semiconductor layer15. However, the present embodiments are not limited to irradiating thetransformed layer 15 c with light for a thermal process. The localthermal process can be performed by arranging a heating wire patternunder the substrate 11 for heating the predetermined region of theorganic semiconductor layer 15 c.

The transformed region can be formed so that it results in variouspatterns.

FIGS. 4 through 17 show various patterns of a transformed region inaccordance with the present embodiments.

In FIGS. 4 through 17, 12 a represents a gate wire of a gate electrode12 for transmitting a gate signal and data-wire 14 a is connected to oneof a source/drain electrode 14.

FIGS. 4 through 7 show a transformed region 15 c having a closed curveshape of a boundary around a channel region 15 a. As shown in FIGS. 4and 6, the closed curve shape of the boundary may be formed to have apredetermined thickness. Also, the transformed region 15 c is formed tohave a closed curve shape of inner boundary for forming the transformedregion 15 c on outside of the channel region 15 a as shown in FIGS. 5and 7.

The boundary of the transformed region 15 c may overlap a predeterminedportion of the gate electrode 12 as shown in FIGS. 4 and 5. Also, theboundary of the transformed region 15 c may be formed on the outsideregion of the gate electrode 12 as shown in FIGS. 6 and 7. The boundaryof the transformed region 15 c may be arranged at the inside of the gatewire 12 a as shown in FIGS. 4 and 5 and the boundary of the transformedregion 15 c may be arranged outside of the gate wire 12 a as shown inFIGS. 6 and 7.

As shown in FIGS. 8 to 15, boundaries of the transformed regions 15 cmay be formed on a pair of substantially parallel lines and the channelregion 15 a is located between the substantially parallel lines.

As shown in FIGS. 8, 10, 12 and 14, the transformed region 15 c may beformed to have a line shape with a predetermined thickness. Furthermore,the transformed region 15 c may be formed on an entire region which isoutside the channel region 15 a and inside boundaries of two transformedregions 15 c are substantially parallel each other as shown in FIGS. 9,11, 13 and 15.

A pair of the substantially parallel lines may be substantially parallelto the gate wire 12 a as shown in FIGS. 8 through 11. Furthermore, apair of the substantially parallel lines may be substantially parallelto one of the wires of the source/drain electrodes 14 as shown in FIGS.12 through 15.

The transformed region 15 c may be formed across the gate electrode 12on the inside of the gate wire 12 a as shown in FIGS. 8 and 9. Also, thetransformed regions 15 c may be formed on outside of the gate wire 12 aand on outside of the gate electrode 12 as shown in FIGS. 10 and 11.

Furthermore, the transformed region 12 may be formed to have an insideboundary across the source/drain electrode 14 as shown in FIGS. 12 and13 and the transformed region 15 c is formed on the outside of thesource/drain electrode 14 as shown in FIGS. 14 and 15.

As shown in FIGS. 16 and 17, the transformed regions 15 c may be formedon two pairs of substantially parallel lines. The channel region 15 a islocated between the transformed regions 15 c formed on the two pairs ofsubstantially parallel lines. One of two pairs of substantially parallellines may be substantially parallel to the gate wire 12 a and the otherof two pairs is substantially parallel to one 14 a wires of source/drainelectrodes 14. As shown in FIG. 16, the transformed region 15 c may beformed across the gate electrode 12 and the source/drain electrode 14.Also, the transformed region 15 c may be formed on outside of the gateelectrode 12 and the source/drain electrode 14 as shown in FIG. 17.

As shown in FIGS. 4 through 17, the transformed regions 15 c furtherincludes a line substantially parallel to a line connecting thesource/drain regions 15 b and the channel region 15 a. Accordingly, awidth of the channel region 15 a can be verified, by the transformedregion 15 c so as to be closer to the design width, or anticipatedwidth.

The thin film transistor (TFT) may have various lamination structures inaddition to the lamination structure shown in FIG. 1.

FIG. 18 is a diagram of a thin film transistor having a laminationstructure in accordance with one embodiment. As shown in FIG. 18, thegate insulation layer 13 is formed on the substrate 11 and the organicsemiconductor layer 15 is formed on the gate insulation layer 13. Afterforming the organic semiconductor layer 15, the source/drain electrodes14 are formed on the organic semiconductor layer 15. The predeterminedregion of the organic semiconductor layer 15 is irradiated with light toform the transformed region 15 c before forming the source/drainelectrodes on the organic semiconductor layer 15.

FIG. 19 is a diagram of a thin film transistor having another laminationstructure. As shown in FIG. 19, a passivation layer 17 is additionallyformed on the organic semiconductor layer 15. The passivation layer 17covers the source/drain electrodes 14 and 14′. The passivation layer 17includes opening units 17 a and 17 a′. The channel regions 15 a and 15a′ may be formed on the opening units 17 and 17 a′.

An organic material, an inorganic material or both can be used forforming the passivation layer 17. The inorganic material includes, forexample, SiO₂, SiNx, AL₂O₃, TiO₂, Ta₂O₅, HfO₂, ZrO₂, BST ((Ba,Sr) TiO₃)and PZT ((Pb,Zr) TiO₃). Also, the organic material can include forexample, a common polymer such as PMMA (polymethyl methacrylate), and PS(polystyrene), a polymer derivative having phenol group, an acrylicpolymer, an imide polymer, an aryl-ether polymer, an amide polymer, afluoric polymer, a p-xylene polymer, a vinyl alcoholic polymer or ablend of any of these. Also, inorganic-organic stacked layers can beused.

It is possible to perform a SAM process (a conventional process forforming a Self-Assembled Monolayer) such as OTS(Octadecyltrimethoxysilane) and HMDS (hexamethyldisilazane) on anuppermost layer adjacent to the organic semiconductor layer 15 of thepassivation layer 17 and also a coating process can be performed on theuppermost layer by using a fluoric polymer thin film or the commonpolymer thin film.

FIG. 20 is a diagram of a thin film transistor (TFT) having a staggeredstructure in accordance with another embodiment.

As shown in FIG. 20, the source/drain electrodes 14 and 14′ are formedon the substrate 11 and the organic semiconductor layer 15 is formed onthe source/drain electrodes 14 and 14′. The organic semiconductor layer15 covers the source/drain electrodes 14 and 14′. The gate insulationlayer 13 is formed on the organic semiconductor layer 15 and the gateelectrodes 12 and 12′ are formed where the channel regions 15 a and 15a′ are faced.

The transformed region 15 c is formed on a predetermined region betweenTFTs 10 and 10′ of the organic semiconductor layer 15.

Accordingly, when irradiation with light or the thermal process isperformed for forming the transformed region 15 c after forming thesource/drain electrodes 14 and 14′ on the substrate 11 and forming theorganic semiconductor layer 15 for covering the source/drain electrodes14 and 14′.

However, the source/drain electrodes 14 and 14′ may be formed afterforming the organic semiconductor layer 15 on the substrate 11 as shownin FIG. 21. In this case, the light is radiated or the terminal processis performed after forming the organic semiconductor layer 15 on thesubstrate 11 and before forming the source/drain electrodes 14 and 14′.

The SAM process including OTS and HMD can be performed on an uppermostlayer adjacent to the organic semiconductor layer 15 of the thin filmtransistors of FIGS. 20 and 21. Also, the uppermost layer of the thinfilm transistors of FIGS. 20 and 21 can be coated with the fluoricpolymer thin film or the common polymer thin film.

The above mentioned transformed region 15 c may be implemented onvarious structures of the thin film transistor.

The above mentioned thin film transistors (TFT) may be included in aflat panel display such as an organic light emitting display and liquidcrystal display (LCD).

FIG. 22 is a diagram of an organic light emitting display having a thinfilm transistor in accordance with an embodiment.

FIG. 22 shows one of the subpixels included in the organic lightemitting display. The subpixel includes an organic light emitting diode(OLED) as a self emitting element, at least one of thin film transistorsand an additional capacitor (not shown).

The organic light emitting display has various pixel patterns accordingto colors emitted from the organic light emitting diode (OLED). In oneembodiment, the organic light emitting display includes pixels for red,green and blue.

As shown in FIG. 22, each subpixel of red, green and blue colorsincludes a TFT and the OLED. The TFT may be one of the TFTs describedabove. However, the present embodiments are not limited to the abovementioned TFTs. The subpixel may have various structures of thin filmtransistors.

As shown in FIG. 22, the thin film transistor (TFT) 20 is formed on aninsulation substrate 21.

The TFT 20 includes a gate electrode 22 having a predetermined patternon a substrate 21, a source/drain electrode 24 formed on the gateinsulator layer 23 and an organic semiconductor layer 25 is formed onthe source/drain electrodes 24.

The organic semiconductor layer 25 includes a source/drain region 25 b,a channel region 25 a connecting the source/drain regions 25 b and atransformed region 25 c. The transformed region 25 c is identical to thetransformed region 15 c in FIGS. 1 through 21 and thus detailedexplanation of the transformed region 25 c is omitted.

After forming the organic semiconductor layer 25, a passivation layer 28is formed to cover the TFT 20. The passivation layer 28 may be formed asa single layer or a plurality of layers by using an organic material(for example PMMA (polymethyl methacrylate), PS (polystyrene), a polymerderivative having one or more phenol groups, an acrylic polymer, animide polymer, an aryl-ether polymer, an amide polymer, a fluoricpolymer, a p-xylene polymer, or a vinyl alcoholic polymer), an inorganicmaterial (such as, for example, SiO₂, SiN_(x), AL₂O₃, TiO₂, Ta₂O₅, HfO₂,ZrO₂, BST or PST) or a blend of organic and inorganic materials.

A pixel electrode 31 is formed on the passivation layer 28 and a pixeldefinition layer 29 is formed on the pixel electrode 31. The pixelelectrode 31 is one of the electrodes of the OLED 30. A predeterminedopening unit 29 a is formed on the pixel definition layer 29 and then anorganic emitting layer 32 of the OLED 30 is formed.

The OLED 30 displays predetermined image information by emitting red,green and blue colors according to flow of current. The OLED 30 includesa pixel electrode 31 connected to one of the source/drain electrodes 24of the TFT 20, a counter electrode 33 formed for covering the entirepixel and an organic emission layer 32.

The pixel electrode 34 and the counter electrode 33 are insulated by theorganic emission layer 32. The pixel electrode 34 and the counterelectrode 33 supply voltage of different polarities to the organicemission layer 32 for emitting light of colors.

A small molecule organic layer or a polymer organic layer may be usedfor the organic emission layer 32. In case of using the small moleculeorganic layer, the organic emission layer 32 may be formed as a singlestructure or a complex structure including a hole injection layer (HIL),a hole transport layer (HTL), an emission layer (EML), an electrotransport layer (ETL) and an electron injection layer (EIL). A copperphthalocyanine (CuPc), N, N'-Di (naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) and tris-8-hydroxyquionoline aluminium(Alq3) can be used for the organic material. The small molecule organiclayer is formed by a vacuum evaporation method.

In case of using the polymer organic layer, the organic emission layer32 includes the HTL and EML. PEDOT (polyethylenedioxythiophene) is usedfor the HTL and a polymer organic material includingpoly-phenylenevinylene (PPV) or polyfluorene is used for the EML. Ascreen printing or an ink-jet printing method can be used for formingthe organic emission layer 32.

However, the organic layer is not limited to being formed by the abovementioned method and materials. Various embodiments can be implementedto form the organic layer.

The pixel electrode 31 works as an anode electrode and the counterelectrode 33 works as cathode electrode. However, the polarity of thepixel electrode 31 and the counter electrode 33 may be switched.

However, the present embodiments are not limited to have the abovementioned structure. Various structures of organic electroluminescentdisplays may be utilized in the present embodiments.

In the case of liquid crystal display (LCD), a bottom alignment layer(not shown) is formed to cover the pixel electrode 31 for manufacturinga bottom substrate of the LCD.

The TFT of the present embodiments may each be equipped with one or moresub pixels as shown in FIG. 22. Also, the TFT of the present embodimentsmay be equipped with a driver circuit (not shown) or other electriccircuits which do not reproduce images.

A flexible plastic substrate is preferably used as the substrate 21 forthe organic electro luminescent display.

As mentioned above, the TFT is distinguished from an adjacent TFT by thetransformed region in the present embodiments. In the presentembodiments, the transformed region having a different size of crystalis formed on the organic semiconductor layer between the TFTs. Thisgives the same result as patterning the organic semiconductor layer.Therefore, the complicated pattern process is not performed formanufacturing the TFT of the present embodiments.

Also, a dry etching process or a wet etching process is not required formanufacturing the TFT of the present embodiments. Therefore,characteristic degradation of the active channel is minimized.

Also, because etching is not required, processing time of a TFT isreduced and the processing efficiency of the TFT is improved.

Moreover, leakage current is minimized by isolating the channel regionfrom the adjacent TFT.

While the present embodiments have been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present embodiments as defined by the following claims.

1. A method of manufacturing a thin film transistor comprising a gateelectrode, a source electrode and a drain electrode, each insulated fromthe gate electrode; and an organic semiconductor layer having a channelregion insulated from the gate electrode and coupled to the source andthe drain electrodes, the method comprising irradiating with light thearea around at least the channel region of the organic semiconductorlayer wherein the conductivity of the organic semiconductor layer isreduced; wherein at least the channel region of the organicsemiconductor layer is not irradiated with light.
 2. The method of claim1, wherein the organic semiconductor layer is irradiated by a laser. 3.The method of claim 1, wherein the organic semiconductor layer isirradiated with ultraviolet light.
 4. The method of claim 1, wherein theorganic semiconductor layer comprises at least one of pentacene,tetracene, anthracene, naphthalene, alpha-6-thiophene,alpha-4-thiophene, perylene, rubrene, coronene, perylene tetracarboxylicdiimide, perylene tetracarboxylic dianhydride, a oligonaphthalene,oligothiophene of alpha-5-thiophene, phthalocyanine including a metal,phthalocyanine not including a metal, naphthalene tetracarboxylicdiimide, naphthalene tetracarboxylic dianhydride, pyromelliticdianhydride, pyromellitic diimide, conjugate polymer containingthiophene and a polymer containing fluorene.
 5. A method ofmanufacturing a thin film transistor comprising a gate electrode; asource electrode and a drain electrode, each insulated from the gateelectrode; and an organic semiconductor layer having a channel re ioninsulated from the gate electrode and coupled to the source and drainelectrodes, wherein the method comprises performing a thermal process onthe organic semiconductor layer at least near the channel region of theorganic semiconductor layer after forming the organic semiconductorlayer, wherein the conductivity of the organic semiconductor layer isreduced; wherein the thermal process is not performed on at least thechannel region of the organic semiconductor layer.
 6. The method ofclaim 5, wherein the organic semiconductor layer comprises at least oneof pentacene, tetracene, anthracene, naphthalene, alpha-6-thiophene,alpha-4-thiophene, perylene, rubrene, coronene, perylene tetracarboxylicdiimide, perylene tetracarboxylic dianhydride, oligonaphthalene,oligothiophene of alpha-5-thiophene, phthalocyanine including a metal,phthalocyanine not including a metal, naphthalene tetracarboxylicdiimide, naphthalene tetracarboxylic dianhydride, pyromelliticdianhydride, pyromellitic diimide, conjugate polymer containingthiophene and a polymer containing fluorene.
 7. A method ofmanufacturing a flat panel display, comprising: forming a thin filmtransistor comprising a gate electrode formed on a substrate; a sourceelectrode and a drain electrode, each insulated from the gate electrode;and an organic semiconductor layer having a channel region insulatedfrom the gate electrode and coupled to the source and drain electrodes;and forming a pixel electrode electrically connected to one of thesource and the drain electrodes of the thin film transistor, the methodcomprises irradiating with light the area around at least the channelregion of the organic semiconductor layer wherein the conductivity ofthe organic semiconductor layer is reduced; wherein at least the channelregion of the organic semiconductor layer is not irradiated with light.8. The method of claim 7, wherein the organic semiconductor layer isirradiated with a laser.
 9. The method of claim 7, wherein the organicsemiconductor layer is irradiated with ultraviolet light.
 10. The methodof claim 7, wherein the organic semiconductor layer comprises at leastone of pentacene, tetracene, anthracene, naphthalene, alpha-6-thiophene,alpha-4-thiophene, perylene, rubrene, coronene, perylene tetracarboxylicdiimide, perylene tetracarboxylic dianhydride, oligonaphthalene,oligothiophene of alpha-5-thiophene, phthalocyanine including a metal,phthalocyanine not including metal, naphthalene tetracarboxylic diimide,naphthalene tetracarboxylic dianhydride, pyromellitic dianhydride,pyromellitic diimide, conjugate polymer containing thiophene and apolymer containing fluorene.
 11. A method of manufacturing a flat paneldisplay, comprising: forming a thin film transistor comprising a gateelectrode formed on a substrate, a source electrode and a drainelectrode, each insulated from the gate electrode; and an organicsemiconductor layer having a channel region insulated from the gateelectrode and coupled to the source and the drain electrodes; andforming a pixel electrode electrically connected to one of the sourceand the drain electrodes of the thin film transistor, the methodcomprises performing a thermal process on the organic semiconductorlayer at least near the channel region of the organic semiconductorlayer after forming the organic semiconductor layer, wherein theconductivity of the organic semiconductor layer is reduced; wherein thethermal process is not performed on at least the channel region of theorganic semiconductor layer.
 12. The method of claim 11, wherein theorganic semiconductor layer comprises at least one of pentacene,tetracene, anthracene, naphthalene, alpha-6-thiophene,alpha-4-thiophene, perylene, rubrene, coronene, perylene tetracarboxylicdiimide, perylene tetracarboxylic dianhydride, oligonaphthalene,oligothiophene of alpha-5-thiophene, phthalocyanine including metal,phthalocyanine not including metal, naphthalene tetracarboxylic diimide,naphthalene tetracarboxylic dianhydride, pyromellitic dianhydride,pyromellitic diimide, conjugate polymer containing thiophene and apolymer containing fluorene.